1. Field of the Invention
The present invention relates to a honeycomb structure.
2. Discussion of Background
In order to convert exhaust gases from automobiles, many technologies have been developed. Due partly to an increase in traffic, it is, however, hard to say that adequate measures have been taken. Controlling exhaust gases from automobiles tends to be further intensified domestically and internationally. Particularly, NOx in diesel exhaust gas is strictly controlled. The reduction of NOx has been attempted by the control of the burning system of an engine, but it becomes difficult for this method alone to sufficiently deal with the problem. As a diesel NOx conversion system for this problem, a NOx reduction system (called an SCR system) that reduces NOx using ammonia as a reducing agent has been proposed.
As a catalyst carrier used for such a system, a honeycomb structure is known. The honeycomb structure of International Publication No. 2005/063653 discloses a honeycomb catalyst formed of honeycomb units obtained by mixing γ-alumina, ceria, zirconia, zeolite, etc., with inorganic fibers and an inorganic binder, then molding the mixture into a honeycomb shape, and after that firing the molded material.
JP-A-08-229412 discloses a honeycomb-shaped catalyst for eliminating NOx in which the volume of pores having diameters in the range of 0.01 μm through 0.03 μm in cell walls accounts for 50% through 80% of the volume of all the pores and the volume of pores having diameters in the range of 0.8 μm through 4 μm in the cell walls accounts for 10 through 30% thereof. Catalyst components of this honeycomb-shaped catalyst should be oxides containing titanium or composite oxides.
The contents of Pamphlet of International Publication No. 2005/063653 and JP-A-08-229412 are incorporated by reference herein in their entirety.